They call it an "unprecedented, monumental step in the direction of further consolidation of Big Media."

Both are veteran critics of media mergers, so the opposition is not a big surprise.

In the 48-page filing, not including apendices, they groups say the deal would "harm competition, impede innovation by online video distributors, threaten innovation in equipment and platforms, and reduce the diversity of information sources and services to the public, all to the detriment of consumers and contrary to the public interest."

"If this deal goes through, we can expect to be hit with more skyrocketing bills and worse service as Comcast gains even more control over what we see online and on TV," said Delara Derakhshani, policy counsel for Consumers Union, in announcing the petition. "The two companies have failed to demonstrate how the merger would serve the public interest. The benefits they claim are overstated, or elusive, or don't depend on a merger, and they are far outweighed by the harms."

Comcast and Time Warner Cable have argued that since their will not be system overlap, their combo is not reducing choice in either broadband or traditional video. But Consumer's Union and Common Cause say that is "too narrow a view of how competition works and how it would be harmed...By the logic of that narrow view, Comcast should be free to acquire every cable and Internet company throughout the country in every market it does not already serve - amassing a nationwide monopoly."

The deadline for for petitions to deny is Aug. 25. Comcast and TWC will have an opportunity to respond to that any other petitions, if any, in reply comments.